Amazonite

Amazonite is microcline feldspar in green to blue-green. The colour was long unexplained and is now attributed to trace lead together with water in the structure, activated by natural radiation — a mechanism closer to smoky quartz's than to a simple transition-metal impurity.

It commonly shows a white grid or streaking, which is not a flaw but the perthitic intergrowth of albite that most microcline contains, exsolved on cooling. In the same way as moonstone, the pattern is a record of how slowly the crystal cooled.

Its colour fades with prolonged heat and, in some material, with strong light.

Opaque green feldspar with two cleavages near ninety degrees and a white grid pattern. The cleavage separates it from jade, turquoise and chrysoprase, which is the group it is most often confused with and sometimes sold as.

Cabochons, beads, carvings and inlay. Used in Egypt from the predynastic period — there are amazonite beads and amulets from before 3000 BC, and the source was probably the Eastern Desert.

A misnomer, and known to be one. It was named for the Amazon River, and no amazonite deposit has ever been found there — the green stones the name was taken from were probably a jade. The name has stuck for two centuries regardless.